A long term study of twilight clouds on Mars based on Mars Express VMC images
Abstract
During twilight, when the sun is below the horizon, clouds and atmospheric dust can still be illuminated by the sun if they are high enough over the surface, as they escape the shadow of the planet. Observations of this direct illumination can be used to determine the minimum altitude for elevated features. Twilight clouds were first observed on Mars by ground-based telescopes, and then by cameras on the Viking orbiters. However, in the last few decades of Mars exploration, most orbiters have been placed in sun-synchronous orbits centered around the afternoon, and thus few observations of the twilight have been collected.
Mars Express is an excellent platform for the study of twilight clouds due to its non-sun-synchronous orbit, The Visual Monitoring Camera (VMC) onboard MEX has a wide Field of View that allows regular observations of the full disk of Mars (usually including the region in dawn) from the apocenter of the MEX orbit. The current VMC dataset includes ~50 000 images distributed across ~3000 observations (each observation consisting of several consecutive images), covering 8 Martian Years. We have developed a pipeline to perform a the systematic study of twilight clouds in VMC images. We find three main groups of recurrent of twilight clouds in a belt around 45ºS. These three groups correspond to the regions of Terra Cimmeria, Terra Sirenum, and Aonia Terra, where the clouds appear mostly in the southern winter. Additionally, some of the highest clouds we find correspond to these regions.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMP036...06H
- Keywords:
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- 0343 Planetary atmospheres;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 6225 Mars;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS;
- 5405 Atmospheres;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS;
- 5445 Meteorology;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS